Clinical and Radiographic Factors Predict the Incidence, Severity and Timing of Vertebral Compression Fractures Following Stereotactic Radiosurgery for Spinal Metastases

Introduction: Vertebral compression fractures (VCFs) are potential complications following spine stereotactic radiosurgery (SRS). However, limited data exists on prognostic factors underlying the incidence, severity, and timing of VCFs following SRS.

Methods: This retrospective cohort study included 938 vertebral bodies (725 spinal metastases) that underwent single- or multi-fraction SRS from 2002-2024. Exclusion criteria included prior lesion-specific surgical intervention (e.g., resection or kyphoplasty) and lack of follow-up. Logistic regression and Cox proportional hazards modeling were used to evaluate predictors (patient demographics, clinical and radiographic parameters, and radiation dosimetry) of VCFs.

Results: The median follow-up was 8 months (range: 1-251). Sixty-nine VCFs (10%) were identified: 36 (5%) were de novo fractures, and 33 (5%) were progressive fractures. The median time to VCF was 6 months (range: 1-83). The 1- and 3-year cumulative incidence of VCFs were 10% (95%CI: 7.5-13) and 17% (95%CI: 13-21), respectively. Forty-four (7%) VCFs required subsequent stabilization surgery. On multiple regression analysis, gross tumor volume >20cc (P=0.048, β: 0.06, 95%CI: 0.00-0.13) and epidural tumor extension (P=0.024, β: 0.08, 95%CI: 0.01-0.15) were significantly associated with the development of a VCF, while only Spinal Instability Neoplastic Score (SINS) >12 (P=0.040, β: 0.11, 95%CI: 0.01-0.21) was associated with VCFs requiring surgical stabilization. SINS >12 (P=0.038, β: 0.12, 95%CI: 0.01-0.23) and lumbar metastases (P=0.014, β: 0.07, 95%CI: 0.01-0.13) were associated with de novo VCF development, while no tested prognostic factors were significantly associated with progressive VCF development. On multivariable Cox regression analysis, gross tumor volume >20cc (P=0.017, HR: 2.77, 95%CI: 1.20-6.39) and epidural tumor extension (P < 0.001, HR: 3.77, 95%CI: 1.73-8.18) were associated with shortened times to VCF development.

Conclusion : This large clinical study of patients undergoing spine SRS clearly identifies those who have an increased risk of developing symptomatic VCFs. These patients may benefit from more frequent clinical and radiological follow-up and possibly prophylactic surgical stabilization.